title: Empirical growth curve estimation considering multiple seasonal compensatory growths of body weights in Japanese Thoroughbred colts and fillies.
abstract: Thoroughbred horses are seasonal mating animals, and their foals are born yearly in spring seasons. In northern regions or countries, the foals generally show a typical seasonal compensatory growth pattern, where their growth rate declines in winter and increases in the next spring. In this study, a new empirical approach is proposed to adjust for this compensatory growth when growth curve equations are estimated, by using BW of Japanese Thoroughbred colts and fillies raised in Hidaka, Hokkaido. Based on the traditional Richards growth curve equation, new growth curve equations were developed and fit to the weight-age data. The foals generally experience 2 major winter seasons before their debut in horseracing. The new equations had sigmoid subfunctions that can empirically adjust the first and second year compensatory growths, combined with the Richards biological parameter responsible for the maturity of animals. The unknown parameters included in the equations were estimated by SAS NLMIXED procedure. The goodness-of-fit was examined by using several indices of goodness-of-fit (i.e., Akaike's information criterion, Bayesian information criterion, -2 log likelihood, and residual sum of squares) for the multiple applications of the subfunctions. The indices indicated the best fit of the new equations including both subfunctions for the first and second compensatory growths to the weight-age data. The shapes of the growth curves were improved during the periods of compensatory growth. The proposed method is one of the useful approaches for adjusting multiple seasonal compensatory growths in growth curve estimations of Thoroughbreds and for the management of young horses during the compensatory periods.
authors.affiliation: Comparative Agricultural Sciences, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Onoda
authors.forename: R
authors.initials: R
authors.lastname: Yamamoto
authors.forename: K
authors.initials: K
authors.lastname: Sawamura
authors.forename: Y
authors.initials: Y
authors.lastname: Inoue
authors.forename: H
authors.initials: H
authors.lastname: Murase
authors.forename: Y
authors.initials: Y
authors.lastname: Nambo
authors.forename: T
authors.initials: T
authors.lastname: Tozaki
authors.forename: A
authors.initials: A
authors.lastname: Matsui
authors.forename: T
authors.initials: T
authors.lastname: Miyake
authors.forename: N
authors.initials: N
authors.lastname: Hirai
mesh_terms: D000375:Aging; D000818:Animals; D003198:Computer Simulation; D005260:Female; D006736:Horses / Q000254:growth & development*; D007564:Japan; D008297:Male; D008954:Models, Biological; D012621:Seasons; D015430:Weight Gain / Q000502:physiology*